The present invention relates to an article, and, in particular, to an article having an embedded electronic device and a method for making the article.
The plastic xe2x80x9ccredit cardxe2x80x9d has seemingly become ubiquitous. Not only are plastic cards in use worldwide for purchasing goods and services, whether through credit or debit type accounts, but they are rapidly coming into use for many other uses, such as membership cards, library cards, identification cards, access cards, driver""s licenses and the like. With the increasing use of plastic cards has come the increasing misuse thereof, whether by thieves or persons seeking unauthorized access or a false identification.
The first innovation to make these ubiquitous plastic cards easier to use and more secure against misuse was the addition of a stripe of magnetic material in which can be encoded information facilitating the use of the cards, such as account numbers and expiration dates, as well as security information, such as personal identifying information and PIN numbers. The magnetic stripe has the advantage of being easy and inexpensive to manufacture and encode. The proliferation of these cards is aided by an International Standardizing Organization (ISO) standard for the dimensions and stripe properties for such cards. Thereafter followed the addition of an embossed xe2x80x9cholographicxe2x80x9d or diffraction grating optical patch that changed color and/or design as viewed from different angles onto the cards. These optical devices had the advantage that they were very inexpensive to manufacture, but the manufacturer needed sophisticated and expensive machinery to do so, thereby making counterfeiting impractical.
Alas, the ingenuity of the thieves and counterfeiters has enabled them to also reproduce magnetic stripe plastic cards and even embossed optical patch security features. To achieve greater security, a more sophisticated information repository was needed that is also more difficult to counterfeit, or at least one that is more expensive and requires sophisticated production machinery. The embedded electronic device, in particular the semiconductor chip, has provided the best solution thus far. Such electronic devices may include a memory device, a microprocessor, or a combination thereof, and are conventionally embedded in a cavity formed in a plastic card blank. Electrical signals are coupled into and out of such embedded electronic devices either by direct electrical contact to contact pads on the plastic card in the case of xe2x80x9cdirect contact typexe2x80x9d cards or tags, or by radio-frequency (rf) signaling between a card reader and a receiver/transmitter antenna embedded in the card in the case of xe2x80x9ccontact-less typexe2x80x9d smart cards or tags. A plastic card including one or more embedded electronic devices is often referred to as a xe2x80x9csmart card.xe2x80x9d
Conventionally, smart cards are commonly made of rigid polyvinyl chloride (PVC), however, PVC is gradually being replaced by polyester thermoplastic (PET) resin. The properties of these thermoplastic resins, particularly the melting temperature, dictate for the most part which of the available manufacturing processing techniques have suitable temperature and time exposures and so may be employed. PVC resin typically softens and deforms at a temperature around 60-80xc2x0 C., depending on the amount of plasticiser used in the processing of the PVC card substrate. Typically, the electronic device is mounted to and is electrically connected to one side of a small printed wiring electronic substrate by wire-bonding connections using very fine gold or aluminum wires. This small substrate is necessary because the bonding of the gold wires must be performed at a temperature of 150-250xc2x0 C. which is higher than the thermoplastic card substrates can withstand. After wire-bonding the input/output connections of the electronic device to the electronic substrate with gold or aluminum wires, the electronic device is then encapsulated to the electronic substrate with a glob of resin for both mechanical and environmental protection. This intermediate electronic substrate with an electronic device wire-bonded thereto forms a module that is subsequently bonded onto a cavity machined or otherwise formed in the card substrate, which bonding is performed at a temperature around 60xc2x0 C.
FIG. 1 is a cross-sectional side view of a prior art smart card 100 of this type. Plastic card blank or substrate 102 has a cavity 104 formed therein. An electronic module 110 includes an electronic device 112 attached to one side of an electronic substrate 114, which may be of type FR4 printed circuit board material, for example. Conventional conductive epoxy that cures at a temperature of about 150xc2x0 C. attaches electronic device die 112 to substrate 114. Input/output connections from electronic device 112 are connected by bond wires 116 to contact pads on electronic substrate 114 which connect to external contacts 118 on the other side thereof. Electronic device 112 is encapsulated to electronic substrate 114 by encapsulant 118 which may be either dispensed thereon or molded thereto, typically at a temperature of about 150xc2x0 C. A quantity of adhesive is dispensed into cavity 104 of card substrate 102 and then module 110 is inserted therein to complete smart card 100. One problem associated with this method of assembly is the need to precisely control the dispensing of both encapsulant 120 and adhesive 106 so that the external surface of substrate 114 when fully inserted into cavity 104 is substantially co-planar with the one surface of card substrate 102. In practice, this is difficult to achieve. In fact, the top of cured encapsulant 120 is typically ground off to obtain the controlled thickness and parallel surface necessary for proper assembly into a card. Another disadvantage results from the individual handling and multiple wire bonds required for each electronic device, and from the separate individual glob-type encapsulation process. Each of these operations increases the cost of conventional smart card 100, so that the cost of each card can be as high as $0.50-$1.00 U.S. per card when purchased by the customer. Little improvement is possible with conventional methods, except possibly by using adhesives that bond and cure faster to reduce the process time required to attach module 110 to card substrate 102. Current production adhesives typically cure at a relatively low temperature, e.g., less than 60xc2x0 C. for a reasonable time, e.g., 30 minutes or longer.
Similar processes of wire bonding and assembling of electronic devices into a smart card are employed for card substrates formed of PET resin. The properties of PET resin differ from those of PVC primarily in the higher softening and deformation temperatures of PET of about 110-130xc2x0 C. With PET resin card substrates, the electronic device module attachment may be performed at slightly higher temperature, for example, around 120xc2x0 C. without causing a major problem. This opens up additional possible uses of smart cards in higher temperature environments, if smart cards having appropriate properties are available, but with the same problems and disadvantages as set forth above for PVC cards.
Direct-contact type smart cards are also limited by the number of contacts that are available between the smart card and the card reader, as well as the durability and reliability limitations of electromechanical contacts. A long-term solution that avoids these limitations of smart card utilizes wireless communication methods to communicate with a contact-less smart card. Because the card need not be in physical contact with the card reader, but only need be xe2x80x9cnearxe2x80x9d the reader, a contact-less smart card is particularly suited important for fare and toll collection, access control, time-attendance, and other conventional smart card applications. The characteristics of the particular RF wireless communication link between the smart card and the card reader determine what is xe2x80x9cnearxe2x80x9d in a particular application, whether that be a matter or inches, feet or yards, or a greater distance.
A typical prior art contact-less smart card 1, for example, a xe2x80x9cData Carrier Having Separately Provided Integrated Circuit and Induction Coilxe2x80x9d of U.S. Pat. No. 5,880,934, is shown in plan and cross-sectional side views in FIGS. 2A and 2B. Prior art contact-less card 1 has two outer substrates 10 on one of which is deposited an induction coil 7 having coil leads 8 formed by one of conventional screen printing an electrically-conductive adhesive, applying an electro-conductive coating by hot stamping, punching out of a metal foil or an electro-conductively coated plastic film. Separately, a module 6 is fabricated by attaching an integrated circuit 4 to contact elements 5 of a substrate of module 6 by wire bonding and covering integrated circuit 4 with a glob of encapsulating material, although integrated circuit 4 could be attached to the substrate of module 6 in a conventional manner by bonding the contact pads thereof to contact elements 5 using electrically conductive adhesive. Module 6 is then attached to top layer 10 by connecting contact elements 5 of module 6 to coil leads 8 of induction coil 7 using electrically conductive adhesive. A conventional card blank having a stepped cavity 3 therein for receiving integrated circuit module 6 is prepared by laminating two inner layers 11 each having an opening 3 of different dimension therethrough that together form a stepped opening 3. Alternatively, one inner layer 11 having a stepped opening 3 formed therein as by molding, machining or hot-forming could be employed, or the inner layers 11 could be laminated to the bottom outer layer 10 before module 6 is inserted into opening 3. Finally, top cover 10 and the prepared card blank of layers 11 are positioned so that module 6 extends into stepped opening 3 and the cover and inner layers 10, 11 are laminated together, for example, between flat plates at a temperature and for a time appropriate for the layers 10, 11 to form a permanent bond of the complete contact-less card 1.
Due to the many separate steps in the manufacture of prior art smart cards, the current cost of a contact-less smart card made by conventional methods is several times more than that of a direct-contact type smart card, and so tends to prevent the wider use of smart card technology. While the cost of the electronic device may be increased slightly by the need for transmitting and receiving circuits, that cost is overshadowed by the cost of packaging and assembling the contact-less card. The reason the packaging cost is quite a bit more than that of contact type cards is principally due to the need for an embedded antenna and a separately packaged and tested module including the electronic device. In particular, the RF loop antenna must be formed on a substrate, whether by attaching a loop of wire or other conductor thereto or by depositing a loop of conventional thick-film conductive ink thereon as described above. Curing the deposited, attaching the electronic device to the substrate by conventional adhesive dispensing, and curing, and adhesively laminating the substrate to the card substrate, all add production steps, time and cost. All this is similar to the problems associated with conventional assembly processing for prior art direct-contact type smart cards.
Accordingly, there is a need for a card that is simpler and less expensive to make and for a method of making cards that avoids the need to individually handle, wire bond and encapsulate electronic devices. It would be desirable that such method lend itself to automated processing as may be suitable for higher-speed and higher volume production than are available under the conventional methods described above.
To this end, the article of the present invention comprises a substrate having first and second opposing surfaces, an electronic device mounted on the first surface of the substrate, and a layer of melt-flowable adhesive on the first surface of the substrate covering the electronic device, wherein the electronic device is encapsulated by the layer of melt-flowable adhesive.
According to a further aspect of the invention, a method of making an article having an electronic device embedded therein comprises:
providing a substrate having first and second opposing surfaces;
attaching an electronic device to the first surface of the substrate;
providing a layer of melt-flowable adhesive proximate the first surface of the substrate of sufficient thickness to cover the electronic device; and
melt flowing the melt-flowable adhesive to encapsulate the electronic device to the substrate.